Quantification of fracture properties and microstructural features of roasted Marcona almonds by image analysis

A method to quantify fracture pattern and microstructural heat damage through image analysis was proposed. The microstructure of Marcona almonds with different degrees of roasting (200 °C; 0, 1.5, 3, 4.5, 6 min) was related with their compression and fracture behaviour. Mechanical tests were performed with a TAXT2 texture analyser. The fracture pattern was characterized by measuring the particle size distribution with image analysis after compression. Light microscopy (LM) and scanning electron microscopy (SEM) were used to observe the changes in the microstructure of the almonds during roasting. The use of image analysis to quantify micro- and macro-structural features proved to be a very useful tool for analysing the crispness/crunchiness behaviour of the samples. The disruption of the inner parenchyma in the samples roasted for longer times proved to be the principal cause of their increased brittleness. The heterogeneity caused by heat degradation contributed to the failure of the material under compression, changing it from a deformable hard solid (raw sample) to a brittle one with enhanced crispy/crunchy characteristics.